Much of what we’ve been seeing since the onset of the Cambrian, Saturday February 27, is the outcome of evolutionary arms races, leading to steady improvements in teeth, claws, armor, and mobility. It may well be that the onset of predation is what triggered the Cambrian explosion in the first place. The paleontologist Geerat Vermeij argues that arms races and escalation – not adaptation to the physical environment – are the greatest cause of progressive evolution.

We’ll see when we start getting into human evolution, biological and social, that enemies – other people especially – and arms races go on being a major motor of change. But arms races and escalation are going to look different in human evolution than they do in most non-human evolution. People are super-cooperators, and violent competition in humans tends to involve more group-against-group competition, with rival groups monopolizing and competing over territory. And in the human analog of predation – the formation of stratified societies, where elites live off the mass of the population – the human “predators” commonly band together under the aegis of the state to regulate their competition. At their best, human elites are more like sheepdogs and less like wolves.

Yet it’s sometimes among refugees from arms races that the greatest evolutionary advances arise: fish moving onto land may have been doing it partly to get to someplace where enemies were weak or scarce. Human analogs might be the early Ionian Greeks fleeing the Dorian invasions, the settlers of Polynesia getting out from under a social order of ranked lineages, or the New England Pilgrims fleeing an un-Godly England. Or Vermeij himself – he is competitively handicapped, having lost his sight at three years old, but has made a distinguished career studying shelled invertebrates by touch.